Air-drying and long-term storage effects on β-glucosidase, acid phosphatase and arylsulfatase activities in a tropical Savannah Oxisol

Air-drying soil samples causes a rapid cessation of microbial activity and is a useful means of storing soil samples and standardizing experiments as moisture levels can be accurately controlled. In contrast to temperate soils, there is little information regarding the advantages and disadvantages of using field-moist or air-dried soil samples in the assessment of enzyme activities in tropical soils. The aim of this study was to evaluate the effects of air-drying and a two-year storage period on β-glucosidase, acid phosphatase and arylsulfatase activities in soil samples from cultivated and non-cultivated clayey Oxisols from the Cerrado region. Cultivated soil samples (0-10 cm depth) were collected from 24 treatments in three long-term experiments and analyzed to determine their enzyme activities and soil organic carbon (SOC). These treatments presented a large range of extractable Mehlich-P values and cumulative corn and soybean yields. Non-cultivated soil samples from four nearby areas with native Cerrado vegetation were also included in the study. In the laboratory, soil samples were divided into two groups. In the first group, soil samples were separated, stored at 7 °C at field moisture levels and sieved through a 4 mm sieve. The analyses were performed within 1 week after sampling. In the second group, soil samples were air-dried at room temperature for two weeks, sieved through a 2 mm sieve and stored for 2 years at room temperature. Average reductions of 26%, 53% and 72%, were observed in the activities of β-glucosidase, arylsulfatase and acid phosphatase in the air-dried long-term stored samples, in both cultivated and non-cultivated Cerrado clayey Oxisols. Air-drying and long-term storage hardly changed the ranking of treatments for β-glucosidase, arylsulfatase and acid phosphatase. However, a reduction in the capacity to detect changes among treatments was observed for acid phosphatase, which prevents the recommendation of air-drying prior to its analyses. As long as the effects of air-drying upon soil enzymes activities are well established, this pretreatment can be used for β-glucosidase and arylsulfatase analyses in the Cerrado clayey Oxisols.